Yes, you can use a physical key from the original deadbolt to lock and unlock your door even when you have a Yale Smart Lock Pro installed.

The Yale Smart Lock Pro retrofits to an existing deadbolt on the interior side of the door. From the outside, the lock looks exactly the same and you can use the original physical key to lock and unlock your door. This is useful if your phone is lost, stolen, or if the battery in your phone dies.

More information about deadbolt compatibility is available here.